Light-duty liquid (LDL) or gel detergent compositions useful for manual dishwashing are well known in the art. Such products are generally formulated to provide a number of widely diverse performance and aesthetics properties and characteristics. First and foremost, liquid or gel dishwashing products must be formulated with types and amounts of surfactants and other cleaning adjuvants that will provide acceptable solubilization and removal of food soils, especially greasy soils, from dishware being cleaned with, or in aqueous solutions formed from such products. Thus, there is a continuing effort by formulators of liquid dishwashing compositions to incorporate additional components into LDL detergents to provide consumers with improved cleaning benefits.
Second, liquid dishwashing products must be formulated to be physically stable and free of adverse heterogeneity. “Physical stability” in this sense refers to the tendency of a liquid composition to remain as a homogeneous solution rather than having one or more components precipitate (if the discontinuous phase is a solid) or separate (if the discontinuous phase is a liquid) out of the liquid. Thus, a useful detergent composition is one that is free of inhomogeneties and is stable under a variety of different service conditions and storage temperatures—previous formulators have found cold temperature stability particularly difficult to obtain. Physical stability not only enhances the appearance and hence the consumer perception of the product, but is also essential to providing effective cleaning performance.
Third, liquid dishwashing products should be formulated to have a viscosity that makes the use of the product convenient and practicable. Thus, a liquid dishwashing composition should not be so thick that it cannot be easily poured out of its container and at the same time not so thin that it is difficult to concentrate onto the surface of a sponge or kitchen article. Liquid dishwashing compositions should also have a favorable “dilution profile”, meaning that as the liquid dishwashing product is further diluted with water, the composition decreases in viscosity. This is in contrast to how many typical liquid dishwashing compositions behave, in which compositions upon first aqueous dilution become more viscous, thus making them not only more difficult to use but also impairing their dissolution. “Dissolution” is another important attribute of liquid dishwashing products. By dissolution is meant the rate at which the liquid dishwashing product mixes with water. Generally it is preferable that a detergent product mix quickly with water so that its detersive benefits are immediately available to the consumer, thus minimizing the amount of time he or she must devote to cleaning tasks.
Fourth, special care has to be taken in formulating liquid dishwashing products which include enzymes so that the enzymes are not degraded or decomposed by their interaction with other detergent ingredients. Enzymes are important components of dishwashing compositions because they offer improved cleaning benefits on protein-based soils and have also been shown to provide consumers with a mildness or skin feel/appearance advantage over other similar detergent compositions which do not contain enzymes. However, it can be difficult to incorporate enzymes into liquid dishwashing compositions because they are unstable in the presence of many standard LDL ingredients, such as citric acid. Also because enzymes are active in the presence of water and because most liquid dishwashing compositions are aqueous, care must be taken that the enzymes are not activated during storage and thus depleted by the time the LDL composition is ready for use.
Given the foregoing, there is a continuing need to formulate manual dishwashing liquids that provide excellent cleaning benefits, have stable formulations over a broad temperature range, and yet have a viscosity and consistency so that they are useful and convenient for a manual dishwashing operation. Accordingly, it is a benefit of the present invention to provide light-duty liquid dishwashing compositions which not only provide improved cleaning benefits, but are also of a convenient consistency and viscosity, are colorless and odorless, stable and serviceable under a broad range of service temperatures and have improved enzyme stability over existing liquid dishwashing composition formulations.